The present invention relates to control equipment and methods for a power generation unit which supplies effective power to a power system connected electrically to the power generation unit for a load unit to which the effective power is supplied.
Generally, it is well known that a circulating current flows between generators when the reactive power in a power system is varied by external disturbances in a system with a plurality of synchronous generators with the same specifications and characteristics connected to the same power system and operated in parallel. Hereinafter, the circulating current will be referred to as a cross current.
An example of a cross-current suppressing system is disclosed in the Japanese Patent Application Laid-open No. 58-54837 (1983).
While it is possible to recover the variation of the reactive power by using the method mentioned above, the recovery method may take several seconds, because it adopts a two-step loop control.
It is desired to instantaneously recover the electric power system when the disturbance of the power system occurs, since otherwise social activities dependent on electrical power are interrupted. A variable speed pumping-up power generation system was developed in order to comply with such a high speed requirement. This variable speed system adopted a secondary excitation induction dynamo electric machine. It becomes possible to recover the effective power of the disturbed power system within some milli-seconds by using the variable speed pumping-up power generation system. When the cross-current flowed between the variable speed generator/motors by the disturbances, etc. in the variable speed pumping-up power generation system under the parallel operation, it is very difficult to eliminate the cross-current in a short time utilizing the prior art techniques mentioned above. Accordingly, the advantages of high speed response of the variable speed pumping-up power generation system are not practically attainable in such systems having a plurality of such variable speed generator/motor units.
Further, when a plurality of variable speed generator/motor units are operated utilizing a same operation control method, resonance or "beat" may occur between the variable speed generator/motors. Accordingly, it is undesirable to operate the plurality of variable speed generator/motor units under the same operation condition.
An object of the present invention is to provide an improved control system for electrical power generating installations having a plurality of variable speed generator/motor units operating in parallel, in which the resonance or the beat does not occur.
In order to achieve this object, a variable speed pumping-up power generation system including at least two variable speed generator/motor units operated in parallel, is divided into at least two groups. Each of the groups is controlled by using physical quantities representing operating conditions of respective variable speed generator/motor units concerned which are different from each other, to which a feedback control is performed, or control quantities different from each other are used in the control equipment of each group, or both of them are combined.
According to the present invention, each group of the variable speed pumping-up power generation system is controlled in a different way or control mode. Therefore, the resonance or the beat does not occur between the groups each including the variable speed generator/motor unit. Further, the cross-current produced by an external disturbance can be quickly eliminated. As a result, the instantaneous recovery of the variable speed pumping-up power generation system becomes possible.
As described above, according to the present invention, the stable operation condition of the variable speed pumping-up power generation system can be maintained, thus the stability of the power system can be improved.